Various types of rotary drill bits, reamers, stabilizers and other downhole tools may be used to form a borehole in the earth. Examples of such rotary drill bits include, but not limited to, roller cone bits, rotary cone bits, rock bits, fixed cutter drill bits, drag bits, PDC drill bits and matrix drill bits used in drilling oil and gas wells. A typical rotary drill bit may include a bit body with an upper portion adapted for connection to a drill string. A plurality of support arms, typically three, depend from a lower portion of the bit body. Each arm generally includes a spindle which may protrude radially inward and downward with respect to a projected rotational axis of the bit body.
Conventional roller cone drill bits are typically constructed in three segments. The segments may be positioned together longitudinally with a welding groove between each segment. The segments may then be welded with each other using conventional techniques to form the bit body. Each segment also includes an associated support arm extending from the bit body. An enlarged cavity or passageway is typically formed in the bit body to receive drilling fluids from an attached drill string. U.S. Pat. No. 4,054,772 entitled “Positioning System for Rock Bit Welding” shows a method and apparatus for constructing a three cone rotary rock bit from three individual segments.
A cone assembly is generally mounted on each spindle and rotatably supported on bearings disposed between the spindle and a cavity formed in the cone assembly. One or more nozzles may be disposed in the bit body adjacent to the support arms. The nozzles are typically positioned to direct drilling fluid passing downwardly from the drill string through the bit body toward the bottom or end of a borehole being formed.
Drilling fluid is generally provided by the drill string to perform several functions including washing away material removed from the bottom of the borehole, cleaning the cone assemblies and associated cutting structures, and carrying formation cuttings radially outward and then upward within an annulus defined between the exterior of the bit body and the adjacent portions the borehole. U.S. Pat. No. 4,056,153 entitled, “Rotary Rock Bit with Multiple Row Coverage for Very Hard Formations” and U.S. Pat. No. 4,280,571 entitled, “Rock Bit” show examples of conventional roller cone bits with cutter cone assemblies mounted on a spindle projecting from a support arm.
U.S. Pat. No. 5,531,681 entitled “Rotary Cone Drill Bit With Angled Ramps” provides an example of a roller cone drill bit with enhanced fluid flow around exterior portions of the drill bit to remove formation cuttings and other debris from the bottom of a borehole to an associated well surface.
Pending U.S. patent application entitled “Rotary Drill Bit With Nozzles Designed To Enhance Hydraulic Performance And Drilling Fluid Efficiency”, Ser. No. 11/466,252 filed Aug. 22, 2006 and published as U.S. Patent Publication No. 2007/0163811A1, noted the benefits of tightly controlled, upward directed fluid flow in a well annulus. Spiraling fluid flow may more effectively lift and remove formation cuttings and other downhole debris.
Prior rotary cone drill bits, including roller cone drill bits, often have support arms with generally symmetrical configurations relative to respective leading edges and trailing edges of such support arms. The trailing edge of prior support arms was often intentionally left open to facilitate cleaning associated cutting structures and removal of cuttings and other downhole debris.